Comments on “a Practical Method for Relating Scalar Concentrations to Source Distributions in Vegetation Canopies” by M. R. Raupach     

Lianhong Gu 《Boundary-Layer Meteorology》1998,87(3):515-524

This paper considers a modification to the localized near-field (LNF) theory for predicting scalar concentrations from source distributions in plant canopies. It is argued that the non-diffusive, near-field part of the transition probability P_n, and thus the near-field contribution of the scalar concentration C_n, in the original theory are simply errors. The (approximate) equality of the sum of C_n and the diffusive, far-field contribution C_f with the total scalar concentration C is not guaranteed in general by this theory. A revision is suggested.  相似文献   

信江流域洪涝指数及其预报   总被引：3，自引：0，他引：3  

陆叔鸣  熊蜀斐  张超美  王欢 《气象》1998,24(11):7-11

采用逐日资料,把定性的降雨集中期在时间上和雨量上进行了量化,形成普遍适用的算式,并提出了雨量集中期的集中度的算式,进而建立了把雨量集中期、集中度与洪涝程度密切联系在一起的单站洪涝指数。在此基础上确定了流域雨量集中期、集中度及信江流域洪涝指数。最后,对信江流域洪涝指数作了预报试验。  相似文献   

对计算土壤和岩石中氡浓度及其表面析出率表面边界条件的讨论     

何斌  过惠平 《铀矿地质》1998,14(5):302-307

本文对求解土壤或岩石中氡浓度及其表面析出率的边界条件进行了探讨。以空气中无穷远处氡浓度为零（空气中无氡源）的自然边界条件代替空气与土壤或岩石交界面氡浓度为零的边界条件,给出了土壤和岩石中氡浓度及其表面析出率的具体表达式。与前人研究结果比较,该式中增加了一项,表面氡析出率缩小了一个倍数。通过对土壤、岩石的具体计算．表明两种边界条件的计算结果有相当的偏差。同时,文中还讨论了在两类边界条件下对流对土壤或岩石中氡浓度及其表面析出率计算的影响。  相似文献   

贵州西部煤层中若干有害微量元素的分布及迁移富集规律   总被引：3，自引：0，他引：3  

焦建伟 《华北地质矿产杂志》1998,13(3):236-242

煤中有害微量元素不仅影响煤的加工利用,而且对生态环境及人类健康有极大危害,本文利用现代分析测试手段,对贵州西部晚二叠世主采煤层中的有害微量元素Ａｓ,Ｆ,Ｈｇ,Ｐｔ,Ｃｄ等的含量,分布赋存状态及其迁移富集规律进行了研究。  相似文献   

Measuring the Spatial Focus of Migration Patterns     

Andrei Rogers  Stuart Sweeney 《The Professional geographer》1998,50(2):232-242

The changing territorial concentration of migration flows is of interest to many geographers, yet we still do not have a widely accepted index of spatial focus. The much used index of migration efficiency has been shown to be an inadequate index of such spatial concentration, and two candidates have been suggested to replace it: the Gini index and the coefficient of variation. Both are examined in this paper, and a comparative assessment is offered. Data from the 1970, 1980, and 1990 censuses are used to illustrate the two measures. An examination of the findings reveals that the coefficient of variation measure indicates higher levels of spatial focus than does the Gini index for states with highly concentrated flows.  相似文献   

太阳辐射和地面气象要素的日环食效应   总被引：1，自引：0，他引：1       下载免费PDF全文

“年月日日环食期间太阳辐射和大气重力波的分析研究”课题组 《地球物理学报》1990,33(4):399-407

本文通过对1987年9月23日日环食期间太阳辐射和地面气象要素等实测资料的分析,指出了在日环食过程中太阳辐射和地面气象要素等的变化,也叙述了日食期间地面臭氧含量的变化;第一次在国内测得了由日食引起的大气重力波,进而讨论了大气重力波的若干特性.  相似文献   

北京南郊观象台2008—2018年PM10质量浓度特征及其与主要气象因子的关系     

于丽萍  张晓春  孟磊  等. 《气象与环境科学》2022,45(1):73-80

利用北京市观象台2008年3月2019年2月PM₁₀质量浓度数据,通过均值、偏差、Daniel趋势检验相关分析及显著性检验等统计方法,结合主要气象因子,分析PM₁₀质量浓度变化特征。结果显示:2008-2018年PM₁₀质量浓度年均值总体呈显著下降趋势,但均未达到国家二级限值标准;春季的质量浓度最大,其次为秋、冬季的,夏季的最小;月均值呈“M”形变化特征。PM₁₀质量浓度总体呈周末的高于工作日的周末效应。PM₁₀质量浓度日变化呈早上及夜间的双峰形特征,各季节峰值出现时间略有差异。PM₁₀质量浓度随着风速的增大呈现先上升后下降的变化,在3.4 m·s^-1时最高,为269.1μg·m^-3。风向为偏东、北或偏南时,PM₁₀质量浓度超过二级限值标准的频次较高。PM₁₀质量浓度与降雪的相关性高于与同等级降水的相关性。  相似文献   

Sub‐surface water contribution to recession flow in a mountain headwater stream system based on single monitoring campaign          下载免费PDF全文

Ram P. Neupane  Joseph D. White  Peter M. Allen  Stephen I. Dworkin 《水文研究》2016,30(6):899-913

Discharge in mountain streams may be a mixture of snowmelt, water from surface runoff, and deep return flow through valley bottom alluvia. We used δ¹⁸O and δ²H, solute concentrations, and ²²²Rn to determine water sources of a headwater stream located at the McDonald Creek watershed, Glacier National Park, USA, during summer recession flow period. We analysed minimal water isotope ranges of ?17.6‰ to ?16.5‰ and ?133‰ to ?121‰ for δ¹⁸O and δ²H, respectively, potentially due to dominance of snow‐derived water in the stream. Likewise, solute concentrations measured in the stream through the watershed showed minimal variation with little indication of subsurface water input into the stream. However, we observed ²²²Rn activities in the stream that ranged from 39 to 2646 Bq/m³ with the highest value measured in middle of the watershed associated with channel constriction corresponding to changes in local orientation of underlying rocks. Downstream from this point, ²²²Rn activity decreased from 581 to 117 Bq/m³ in a series of punctuated steps associated with small rapids and waterfalls that we hypothesized to cause radon degassing with a maximum predicted loss of 427 Bq/m³ along a 400 m distance. Based on mass balance calculations using ²²²Rn activity values, streamflow, and channel characteristics, we estimated that groundwater contributed between 0.3% and 29% of total flow. Overall, we estimated a 5.9% of groundwater contribution integrated for stream reach measured at McDonald Creek during recession flow period. Finally, a lower mean hyporheic flux of 14 m³/day was estimated compared to the groundwater flux of 70 710 m³/day. These assessments highlight the potential for radon as a conservative tracer that can be used to estimate subsurface water contribution in mountain streams within a complex geologic setting. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Comparison of different numerical approaches to the 1D sea-ice thermodynamics problem     

《Ocean Modelling》2015

The vertical one-dimensional sea-ice thermodynamic problem using the principle of conservation of enthalpy is revisited here using (1) the Bitz and Lipscomb (1999) finite-difference approach (FD), (2) a reformulation of the sigma-level transformation of Huwald et al. (2005b) (FV) and (3) a Finite Element approach also in sigma coordinates (FE). These three formulations are compared in terms of physics, numerics, and performance, in order to identify the best choice for large-scale climate models. The BL99 formulation sequentially treats the diffusion of heat and the changes in the vertical position of the ice-snow layers. In contrast, the FV sigma-level transformation elegantly treats both simultaneously. The original FV formulation suffers however from slow convergence. The convergence can nonetheless be improved significantly with a few simple modifications to the original code. The three formulations are compared following the experimental protocol of the Sea Ice Model Intercomparison Project for ice thermodynamics (SIMIP2). It is found that all formulations converge to the same solution. The FD approach, however, suffers from the added cost of the remapping step at large number of ice layers (we include in the appendix an optimized version of the FD code–written by one of the reviewer–that resolves this issue). Finally the FE formulation results in a sub-surface temperature over-estimation at low resolution, a problem which disappears at high resolution. Hence, only FD and FV are found suitable for climate models.  相似文献   

Predicting longitudinal dispersion coefficient in natural streams by artificial intelligence methods     

Z. Fuat Toprak  Hikmet Kerem Cigizoglu 《水文研究》2008,22(20):4106-4129

In this study, three artificial neural network methods, i.e. feed forward back propagation, the radial basis function neural network, and the generalized regression neural network are employed to compute the longitudinal dispersion coefficient in order to evaluate its behaviour in predicting dispersion characteristics in natural streams. These methods, which use hydraulic and geometrical data to predict dispersion coefficients, can easily be applied to natural streams and are proven to be superior in explaining their dispersion characteristics more precisely than existing equations. This method of predicting the longitudinal dispersion coefficient in river flows was tested on 65 data sets, obtained by researchers from 30 rivers in the USA. Results using the models are compared with results obtained in many other studies, and are shown to be more accurate than the other methods considered. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献